Marking a Milestone

Every hundred thousand years or so, a large asteroid or comet hits the Earth. The explosive force of the impact sends tons of material into the air and punches a big hole in the crust. We don’t see a lot of these old craters, however, because Earth is a dynamic environment — wind, water, and tectonic plate shuffling constantly changes the appearance of the surface. Over time, many impact craters become altered or buried deep underground.

One such buried crater is underneath Chesapeake Bay in Virginia. Carved out 35 million years ago, the crater now can only be accessed by intensive drilling. In November, Aaron Gronstal, a microbiology student at the Open University in the United Kingdom, visited a drilling project at the Chesapeake crater. His goal: to discover what sort of microbes may now live deep underground in the ancient impact environment. This portion of his journal is the final part of a 4-part series.

Today was a rainy day on the eastern shore, although the heavy rains that had been forecast never came. Instead, we were covered by a thick gray haze that dripped steadily down and didn’t show any sign of dissipating. The weather cast an appropriately dismal atmosphere, as today the core barrel jammed inside the hole. That means the drillers need to bring everything up again and fix the problem before they can dig any further. So drilling is on hold from now until at least midnight. You could say the bad weather has brought with it a string of bad luck, but the truth is these are typical problems that occur when drilling.

Sample team at work near Chesapeake site.Credit: Aaron Gronstal

In the biologists’ corner, we’re hoping that as long as they’re removing the barrels, we’ll be able to get a pump down and take a water sample from inside the crater. It may not be possible, however, if part of the hole is clogged.

In the absence of work, the researchers are trying to come up with activities to keep everyone occupied. Currently, the residence is full of sleeping ‘night-shifters,’ so the television is off-limits. Unfortunately, I’ve finished reading the book I brought with me — "The Satanic Verses," by Salman Rushdie. I had been avoiding reading it until now — when I was a student at the University of California at Berkeley, it was the book everyone was doting over. In the end they were right, it’s fantastic.

The rain prevents walks through the woods or along the beach. So for me, it looks to be a relaxing day of computer solitaire.

November 22, 2005

We were woken early this morning by blistering winds coming off of Chesapeake Bay. They were so strong, in fact, that the power in the house went out mid-morning, right as I was brewing my pot of coffee. With the street lights out and all the store windows as dark as the low clouds overhead, the drive to the dig site took on an ominous air.

Upon arrival, however, our mood was quickly lifted by two groups of high school students on a geology field trip. Although the night shift had passed an uneventful night with no cores, all the young and interested minds wandering about the trailer kept our spirits high. The students were on site most of the day, learning about asteroid impacts and the drilling project first-hand, and they offered us a welcome departure from the normal routine. Scientists are always happy to discuss their projects, and a few of the researchers here have a knack for chatting enthusiastically for hours and hours.

The drill became active again shortly after our arrival today, and the bit was being lowered into the hole as we drove up. The promise of finally getting back to work on the cores offered additional relief from the dreary weather.

Today was my last full day on the drill site, so I was especially anxious to get more biology samples before leaving tomorrow morning. The first few cores to come up after changing the drill bit, however, were nothing but mud and rocks that had fallen into the hole when the core barrel was removed. We were told that there could be around 60 feet of this material to dig through before we make it back down to the bottom of the hole. This, of course, meant that we might not see a new core before midnight.

It was almost the end of our shift when we got some good news. A new core had been brought to the surface. It’s small and consists of hard, packed quartz, but it’s a new core nonetheless. I decided to stay late into the night and wait for the next core, to try to get one more biology sample before I leave.

But the next core to make it to the surface was again composed of hard, packed rock, so it wasn’t possible to take a biology sample. It’s disappointing, but at least the drilling is continuing and we’re slowly pushing closer to the ‘mile deep’ mark for the hole. I’m now heading home to get some sleep before leaving for D.C. in the morning.

November 23, 2005

In my last few hours on the eastern shore, after leaving the residence I stopped by the drill site to check their progress. More cores had made it up last night, and they’re fantastic. The drill passed through quartz and rock, and is now back into more sandy material.

A new group of researchers has been trained to take over collection of the biology samples, and this means that we can keep getting samples as long as the drilling continues. The other good news is that the hole is now at 5,265 feet, only 15 feet shy of a mile, and the cores are getting larger each time one is brought to the surface.

At the site, I gave the lab one last cleaning and collected my things. The samples that I’ve collected during my time here were transferred to Styrofoam coolers. They’ll be traveling back to D.C. with me, where they’ll then be shipped back to my university in England. The next few months of my life will be spent examining this material under a microscope, finally getting a look at what kinds of microbes live deep in the Chesapeake Bay impact crater. It will be many months before our experiments are finished, but eventually they’ll tell us a great deal about life in the salty subsurface of this unique environment.

After reaching D.C. and getting my samples into storage at the USGS, I called the drill site to check on their progress. The mile mark was finally passed at around 1pm. I may not have been able to see the ‘mile stone’ in person, but an email from the site at least lets me enjoy the celebration vicariously though photographs. It’s a great achievement for both the researchers and drillers, and knowing that this goal has been reached, I can now sit back and relax on my flight home.

Editor’s Note: On December 4, 2005, the crater-drilling project reached a final depth of 5,795 feet (1.1 miles). The team recovered a complete succession of cores from the post-impact sediments above the crater, rocks broken up during the impact, and rocks from the crater floor. Click here to read the USGS announcement.